Two patients with leprosy and the sudden appearance of inflammation in the skin and new sensory loss.

Leprosy is a chronic infection caused by Mycobacterium leprae that affects the peripheral nerves, skin, and potentially other organs [1]–[5]. Although the worldwide prevalence of leprosy has decreased in the era of multi-drug therapy (MDT), the global detection of new cases of leprosy remains a concern, with more than 250,000 new cases of leprosy reported in 2007 [3]. The precise mechanism of transmission of leprosy has not been conclusively defined; however, it is likely that this occurs through respiratory secretions by untreated borderline lepromatous and polar lepromatous cases [1],[5]. Target cells of infection are macrophages, histiocytes in the skin, and the nonmyelinating and myelinating Schwann cells in the peripheral nerve, leading to axonal dysfunction and demyelination [6]. Nerve injury plays a central role in the pathogenesis of leprosy, leading to functional impairment and deformity of hands and feet and the eyes [1],[6]. Leprosy is diagnosed by definite loss of sensation in a hypopigmented or reddish skin patch, a thickened peripheral nerve with loss of sensation and muscle weakness in the affected nerve, and presence of acid-fast bacilli on skin smear or biopsy [1],[4]. The immunological response to M. leprae mounted by the host will determine the different potential clinical states. The Ridley-Joplin system uses clinical and histopathological features and the bacteriologic index and includes the polar categories (lepromatous [LL] and tuberculoid [TT]) and the borderline states (borderline tuberculoid [BT], borderline borderline [BB], and borderline lepromatous [BL]) [1] (Table 1). In the polar tuberculoid category, a Th1 type cell–mediated immune response with a low bacterial load is seen. Lepromatous states are characterized by low cell-mediated immunity and a higher bacterial load [5] (Table 1). Clinically, patients with tuberculoid leprosy have a single or very few hypopigmented macules or plaques with a raised edge; they are dry, scaly, hairless, and have reduced sensation; and only a few peripheral nerves are commonly enlarged [1]. Lepromatous leprosy is characterized by widely and symmetrically distributed skin macules, nodules, erythematous papules, and diffuse skin infiltration; thickened peripheral nerves are more frequently identified. Borderline states represent a mixture of signs and symptoms of the polar categories [1]. Table 1 World Health Organization System and Ridley-Joplin Classification and Type of Reaction.